Invoking the java compiler from programs

Question

HI, I'm a high school java student in the AP Java course. A project that I have been interested in for a while is making a simple IDE, but to do this I need to compile and run programs from within my program.
What I have tried:
The method Compiler.compileClasses("name of file i wanted to compile");
The method System.loadLibrary(System.getProperty("java.compiler"));
The JavaCompiler class in javax.tools. this is my source code.
import javax.tools.*;
public class CompileTest
     public static void main(String[] args)
          String fileToCompile ="Test.java";
          JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
          int compilationResult =     compiler.run(null, null, null, fileToCompile);
          if(compilationResult == 0)
               System.out.println("Compilation is successful");
          else
               System.out.println("Compilation Failed");
After this threw NullPointerExceptions I put the line System.out.println(ToolProvider.getSystemJavaCompiler()); and the output was null.
Any help would be appreciated.
Also, if anyone knows how to run the subsequent class file, that would also be a big help

Answer 1

To run the program, load the class file with a classloader, which will give you a Class object. You then use reflection to find the public static void main(String[] args) Method object, then use Method's invoke method to call main.
You should deal with any exceptions from the program so that it doesn't break your IDE.
It would probably be a good idea to run the program in its own classloader which you could trash after it finishes running so you don't leave resources hanging around.
And finally you probably need to deal with the case where the program calls System.exit(). That could be tricky. (translation, I haven't the foggiest idea how to handle it but I'm sure its possible).
Also there is the issue of background threads (non daemon and daemon) running after main completes. What ya gonna do?
Runtime.exec() is looking mighty attractive right now.
Bruce